This invention relates to an internal telephone monitoring system for confirming a visitor before the visitor opens a door or otherwise enters a building. Heretofore systems of this type have not been effective enough for the scrupulous or positive confirmation of the visitor, and in cases where a large number of devices capable of utilizing the monitoring system to confirm the visitor are employed, the cost of the system therefor becomes quite expensive. Furthermore, a visitor who is not acquainted with the subscribers may have free access to the internal telephone for calling up at random, thereby resulting in another disadvantage. A visitor confirmation system would be desirable in this case for the reason that a visitor can be confirmed in a positive manner; however, none of the related systems presently available are suitable for a visitor confirmation system due to the considerably high cost thereof. It is a key point required by visitor confirmation system that such a system enable a visitor to call up any one of the subscribers constituting a single group such as a research laboratory having many offices or an apartment building where a large number of devices are installed to confirm a visitor. At the same time it is desireable to prevent other subscribers from listening to the corresponding conversation and the system showed be properly developed to make it available at low cost and be well capable of being widely used. In terms of the aforementioned point, the purpose of the present invention lies in providing such a visitor confirmation system which is adapted to be used with a conventional community television system (CATV or MATV) or telephone system installed in a unit building or in a unit area.
Although prior art internal telephone systems can be operated by making free access thereto to enable anyone to call any one of the subscribers constituting a group, whether or not a visitor is an acquaintance, it is impracticable to prevent the visitor from calling the subscriber. In case a telephone system is used for calling a subscriber no one else other than such a visitor can call the subscriber. To put it another way, such a visitor who knows at least the personal telephone number of the person to be called can call anyone in a building. Even though a visitor tries to call one of the subscribers in the building at random, the probability of ringing a telephone in the building is virtually zero, and the visitor only rings a telephone installed outside the building. Therefore, no visitor who does not know the telephone number of any of the subscribers can communicate with any other subscriber in the building, nor can he enter the building.
A method to prevent the random use of a visitor confirmation system by calling personal telephone numbers (including an intermural telephone number), for the purpose of protecting a group of subscribers constituting a unit building, or a unit area in a larger sense, as set forth above, still remain to be developed; however, such a system is highly desirable in view of the practical uses thereof.
An object of the present invention lies in providing a visitor confirmation system utilizing personal telephone numbers which is capable of preventing random calls of such a visitor who is not an acquaintance of the subscriber. Accordingly, the present invention makes use in a novel manner of a conventional community television reception system (CATV or MATV) and/or telephone system.
Another object of the present invention lies in providing a visitor confirmation system which is capable of permitting a caller to call one of the subscribers on the same circuit of a CATV or a MATV without interference to the other subscribers and/or in case a telephone system is used jointly in connection therewith, the present invention has a function of preventing other persons from listening in on the conversation on the telephone line.
Still another object of the present invention lies in providing a visitor confirmation system as set forth above and having an additional function of informing a subscriber, if the subscriber's telephone line is busy, of the presence of a visitor by reproducing an image of the visitor on the subscriber's monitoring television receiver.